U bolt "chain plates" for shrouds (mast side stays)

[Yara50]

Just a quick note to remind everybody that the side stay U bolts are subject to crevice corrosion. This means that they might look perfect above the deck, but in the area which is buried in the deck, the horrible phenomenon of crevice corrosion can occur, which can slice through the steel like a knife. It is caused by tiny amounts of water getting in the gap, but no oxygen, so sealing is important. If you lose one of these bolts your mast will fall down!

It is therefore a good idea to remove and inspect these bolts, and when replacing, ensure that the sealing in the deck is 100%.

More info on Careel site:
http://www.careel.com/forum/viewtopic.p ... light=bolt
http://www.careel.com/forum/viewtopic.p ... ight=bolts

[Ozzie]

Good Stuff Ian
... mine are being done with the standing rigging. By the way dont buy automatically from chandlery outlets. I get my SS from Newcastle High Tensile Nuts and Bolts. They only sell good quality stuff as they supply local industry and building firms. Because they buy in crates not bubble carded plastic their prices are brilliant. And they are more than happy to get you one bolt from the warehouse. In fact they are all a happy bunch, must be something in the warter cooler. Most cities would have a similar bulk fittings supplier, check it out you may save a bundle

[Yara50]

My recommendation for top quality:
http://www.trailersailerplace.com.au/ph ... 35#p109535
http://www.wichard.com/contact-us.html
http://www.wichard.com/fiche-A|WICHARD| ... 00-ME.html

[cruiserpete]

Yes, a timely reminder.
Had I not been in the process of refurbishing my I563 I would not have discovered this in time....until to late when my mast may have come crashing down...luckily I discovered it.
Replacing with the Witchard waterproof U bolt as it looks fantastic and is reasonably priced
My Port side U bolt was most certainly a victim of crevice corrosion.





Worth the inspection just for the piece of mind

[Andrew]

Great subject and thanks for the posts and pics,

I should have listened to this and done some preemptive maintenance..But anyway, went out on test sail No1 in old Teria. Besides the centerboard drop line remaining slack.. the main thing was the chainplate u-bolt half-failure while sailing. It went with a resounding high tension twang sound and boat shudder, soon saw that the windward chain-plate u-bolt had lifted about 3 mm off the deck on one side, tweaked to the potential problem quickly thanks to the info in these posts. We let fly, lowered sails, motored to a calm anchorage nearby and lowered the mast before motoring back to the ramp.

When i pulled the u-bolt out, it looked almost exactly like your pics! We were lucky the other half of the bolt held and the mast didn't come down. It was about a 15 knot breeze and happened as we came up hard on the wind in flat water.

[Andrew]

Some more Pics of the Chainplate u-bolt failure and replacement

Fatigue fracture and crevice corrosion closeup

Some bending had occured

The small rust stain on deck should have been the tell tale sign..

[Andrew]

The new u-bolts were off the shelf at Rosshaven marine - Ronstan M8 316 stainless, about $25 each. Replaced both sides with silicone sealant under top plate.

Ronstan M8 316ss U-bolt

[Peter T]

Hello All, this is a VERY interesting problem. If you take a look at all of these U bolts that have failed, you see one thing that stands out. There is only corrosion on one side or one leg of the U bolt. This means that there MUST be electrolysis taking place. Why otherwise would it happen this way. I note that some have obtained their replacements from various sources. Be very very careful what you use. I will bet pounds to pennies that there is a difference in the metallic alloy between the U bolt, the nuts used and the flat plate that sits on top of the deck. This plate I believe is the critical piece. If this plate is say 304 stainless and the U bolt is 316, then it is possible to get electrolysis between the U bolt and the plate and it will always be worse under the plate where salt water can be trapped. What you have here is a small battery. An anode, a cathode and an electrolyte ( salt water ). The way these things are made is what is wrong with them. The U bolt will have a punching in either of the straight sections of the U bolt to stop the plate from sliding too for up the bolt. The electrical connection between the bolt and the plate would be of some resistance so voltage could build across these two items. I would make my own Ubolts from 316 stainless and make the plate out of 316 also. I would then weld ( with 316 stainless rods) the flat bar to the U bolts on either side. This will negate any electrical resistance between the metals. This way there is no possible way to get electrolysis within the bolt. It must be fitted with heaps of sealer and removed and inspected annually. Only then will you have no further problems with them.
Hope this makes sense as I am sure this is what is going on.
Regards Peter T

[Peter T]

Witchards Waterproof U bolts look ok, but the plate is still a seperate piece. I like the idea of the seal over the top, but I would still like to see the plate welded to the U bolt but I doubt if that could be done without ruining the seal

Regards Peter T

[Ozzie]

Just a theory, but I would also wonder if enclosing your vessel under a nice warm humidity creating tarp at home would have an effect on the creation of crevice corrosion. When I replaced my u bolts many years ago they were visually fine. And, by that stage they had been out on the mooring for quite a few years. Of course there is no cover there and a lots of drying wind and sunshine. ( still replaced them)

I now have a tarp to protect my windows but it’s tented to provide ventilation for my cored deck and by extension such fittings.

As stated, this is a theory but worth a mention.